This invention relates to a system for discerning foreign objects not readily discernible to the eye, such as minute glass particles, in the bottom of glass jars, particularly the type of jar whose internal bottom surface is characterized by a peripheral concave region and a central convex hump.
During the packaging of food in glass jars on a production line, the jars are subjected to a number of operations, any of which has the potential of causing breakage. Typically, the jars are inverted and washed, filled, capped, and labelled prior to packing in cases. It will be noted that a number of these operations occur during the time that the jars adjacent to a jar that is broken are open. Thus, there is the danger that glass fragments from the broken jar will find their way into the adjacent jars. Ingestion of food containing such glass fragments, especially by an infant, has potentially catastrophic consequences, and must be scrupulously avoided.
When a broken jar is detected, it is sound procedure to stop the production line and inspect a number of jars that passed through the line on either side of the broken jar. At least several hundred jars on either side of the broken jar are typically inspected. Additionally, even if the broken jar itself is not detected at the time of breakage, standard quality control checks for broken glass are made at frequent intervals and the line can be stopped in order to inspect jars that have been handled during the immediately preceding interval.
Several schemes for inspecting jars on a production line basis are known. However, most of these prior art methods relate to the inspection of empty jars with open mouths. Such prior art methods are wholly unsuitable for inspecting closed jars containing food. Yet, it is closed, full jars that need to be inspected when a broken jar is discovered at some point on the production line.
Many of the prior art methods of inspecting jars require that the jar be rotated during inspection in order to render visible foreign material in the bottom. This is especially true where the inner surface of the jar bottom has a central convex hump. Such rotation of the jar necessitates additional handling and registration which slow down the process, making it difficult to inspect a large number of jars in a reasonable time. Moreover, the additional handling itself increases the chance of further breakage.